Data storage devices may be used in computers and other electronic equipment to store information in the form of data bits. Early data storage devices included computer punch-cards wherein the data consisted of holes with millimeter dimensions. The punch-cards were fed into a computer and the data on the punch cards was read. Today, the millimeter-sized holes have been replaced with much smaller data bits. As the data bits keep getting smaller and smaller, the bits may be positioned closer and closer together and the density of the data stored on a data storage device can be increased. When the data bits are of micrometer, sub-micrometer, or nanometer dimensions, the data storage devices may be referred to as ultra-high-density data storage devices.
FIG. 1 illustrates an ultra-high-density data storage device disclosed in U.S. Pat. No. 5,557,596 to Gibson et al. (the '596 Patent), incorporated herein in its entirety by reference. The ultra-high-density data storage device includes a set of field emitters 100, a data storage layer 110 that is located below the field emitters 100, a micromover 120 that holds the data storage layer 110 below the field emitters 100 and that can position the data storage layer 110 at desired locations relative to the field emitters 100, and electrical connections 130 that can supply energy to the field emitters 100. When supplied with energy, the field emitters 100 can bombard the data storage layer 110 with electron beams and can transform nanometer-scaled portions of the data storage layer from unwritten data bits, designated in FIG. 1 by the reference numeral 140, to written data bits, designated by the reference numeral 150. This transformation occurs via a writing process that will be discussed below.
When writing data to the data storage layer 110, respective field emitters 100 are energized, through the electrical connections 130, and are made to bombard the selected unwritten data bits 140 with electron beams. During the writing process, the electron beams are of sufficient power density to transform the bombarded unwritten data bits 140 from a first material state (e.g. a crystalline state, which may be assigned a “0” value) to a second material state (e.g. an amorphous state, which may be assigned a “1” value). Hence, a data bit having a value of “1” can be written to and stored on the data storage layer 110 by bombarding a crystalline, unwritten data bit 140 and by appropriately cooling the data bit 140 to form an amorphous, written data bit 150, respectively.
When erasing data from the data storage layer 110, respective field emitters 100 are energized, through the electrical connections 130, and are made to bombard the selected written data bits 150 with electron beams. During the erasing process, the electron beams are of sufficient power density to transform the bombarded written data bits 150 from a second material state (e.g., an amorphous state, which may be assigned a “1” value) to a first material state (e.g., a crystalline state, which may be assigned a “0” value). Hence, a data bit having a value of “0” can be restored on the data storage layer 110 by bombarding an amorphous, written data bit 150, thereby appropriately heating the data bit 150 to form a crystalline, erased data bit 140.
When reading data from the storage layer 110, the field emitters 100 again bombard the data bits 140, 150 with electron beams. However, instead of bombarding the data bits 140, 150 with electron beams that have sufficient energy to transform the data bits 140, 150 between the first and second material states discussed above, the field emitters 100 bombard the data bits 140, 150 with relatively low-power-density electron beams that do not effectuate a transformation but that do effectuate identification. Then, the interactions between the low-power-density electron beams and the data bits 140, 150 are monitored in order to read data.
During the reading operation, the low-power-density beams interact differently with unwritten data bits 140 than with written data bits 150. For example, a low-power-density beam may generate fewer secondary electrons when bombarding a crystalline, unwritten data bit 140 than when bombarding an amorphous, written data bit 150. Therefore, by monitoring the interactions between the relatively low-power-density beam and the data bit 140, 150 that the beam is bombarding (e.g. by monitoring the number of secondary electrons generated), it becomes possible to determine whether the bombarded data bit 140, 150 is storing a “1” or a “0” value and to read data stored in the data storage layer 110.